#define _CRT_SECURE_NO_WARNINGS 1

/**
 * Definition for singly-linked list.
 * struct ListNode {
 * int val;
 * ListNode *next;
 * ListNode() : val(0), next(nullptr) {}
 * ListNode(int x) : val(x), next(nullptr) {}
 * ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution
{
public:
	ListNode* mergeTwoLists(ListNode* l1, ListNode* l2)
	{
		if (l1 == nullptr) return l2;
		if (l2 == nullptr) return l1;
		if (l1->val <= l2->val)
		{
			l1->next = mergeTwoLists(l1->next, l2);
			return l1;
		}
		else
		{
			l2->next = mergeTwoLists(l1, l2->next);
			return l2;
		}
	}
};